As is known, CBTC systems determine the position of the train using transponders (also called balises) along the track at regular locations. These electromagnetic devices are used as reference points to position the train with a precision of 1 meter or less. Between two transponders, the CBTC on-board vital computer determines the change of position of the train using data from wheel rotation sensors and/or inertial sensors. The safety of the calculation of the position of the train relies on having multiple sensors of each type and performing within an on-board vital CBTC computer a safe vote procedure, i.e. comparing the data coming from different sensor in order to discover anomalies. Installation of an on-board CBTC computer and its peripherals (transponder reader, tachometer or speed sensor, inertial sensors) is thus a delicate operation, and maintaining these equipments is expensive due to the required hardware redundancy for safety.
Furthermore, CBTC systems typically allow trains to run at optimized intervals that are much closer than what traditional systems using traffic signals allow. As a consequence, installing CBTC often has the side effect of requiring traditional signals to be “cancelled” (i.e. updated for indicating to the driver that said signals have not to be respected) when a CBTC train is approaching (otherwise, the driver may be required to run through a red signal). This is done by adding a new aspect to the signal, i.e. changing or modifying the existing signals. This can be a significant cost and scheduling problem for CBTC deployment. It also increases the cost of maintenance, because in case of a signal failure leading to the unavailability of the “cancel” aspect, the availability of the system will be affected.
In the U.S. Pat. No. 8,233,662 B2, it is discloses a system comprising a camera positioned on a railway car, and adapted to acquire light signals emitted from light transmitters that are installed along the railway. This solution requires an upgrade (also known as revamp) of the railway signals or the installation of new signals along the railway tracks, by increasing the time necessary to deploy a CBTC system on an existing transport network.